Method for light regulation of morphology and conduction enhancement of single gold nanowire plasmonic waveguide

Abstract

The application discloses a kind of light regulation single gold nanowire plasmonic waveguide morphology and conduction enhancement method, belong to nanowire photonic device processing technical field.The method includes: preparation gold nanowire;Single gold nanowire sample is constructed;Gold nanowire is activated and handled on surface;In chloroauric acid reaction environment, single gold nanowire end is irradiated using focused laser, and local plasmon is used to enhance electromagnetic field to induce Au ion to be preferentially reduced and deposited at gold nanowire end, to realize the remote light induced regulation and control to gold nanowire end morphology.The local field of gold nanowire end can be effectively enhanced by the application, the coupling efficiency of incident end light to surface plasmon and the scattering efficiency of exit end surface plasmon to photon are improved, so that the plasmonic waveguide conduction performance of single gold nanowire is significantly improved.The application has the advantages of simple operation, good controllability, high local regulation precision and obvious waveguide enhancement effect.

Description

Technical Field

[0001] This invention belongs to the field of nanowire photonic device processing technology, and more specifically, relates to a method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide. Background Technology

[0002] As optoelectronic integrated devices become increasingly miniaturized, traditional dielectric waveguides are limited by the diffraction limit, making it difficult to effectively confine optical fields at subwavelength scales. Surface plasmon polariton (SPP) waveguides can overcome this limitation, among which one-dimensional metallic nanowire waveguides have attracted much attention due to their strong localized field enhancement properties.

[0003] Silver nanowires exhibit low transmission loss but are prone to oxidation, leading to a continuous decline in transmission efficiency and poor stability. Gold nanowires are chemically stable, but suffer from high ohmic loss in the visible light band. In particular, single gold nanowires synthesized using the polyol method often retain a polyvinylpyrrolidone (PVP) coating layer on their surface, resulting in relatively simple structures at both ends. This limits the coupling efficiency between incident light and surface plasmons, and also leads to low radiation output efficiency after the surface plasmons propagate to the nanowire ends, thus restricting the overall transmission performance of gold nanowire plasmon waveguide devices. Therefore, improving the transmission efficiency of gold nanowires without compromising their inherent properties is a crucial issue.

[0004] Existing methods, such as coating with gain media, utilizing coupling structures, or optimizing excitation conditions, often require the introduction of additional materials or complex processes, making it difficult to achieve in-situ morphology control of single gold nanowires. Photoinduced gold deposition technology, in a chloroauric acid solution, utilizes the photothermal and near-field effects of a focused laser to achieve in-situ deposition of gold on the surface of nanowires, offering advantages such as simple processing and preservation of intrinsic properties. However, a systematic approach combining photoinduced gold growth with morphology control and conduction enhancement of single gold nanowire plasmonic waveguides is currently lacking, and the relevant process parameters and mechanisms remain unclear.

[0005] Therefore, how to effectively control the end structure of a single gold nanowire to enhance the local electromagnetic field at the end, improve the energy conversion efficiency between photons and surface plasmons, and thus enhance the transmission signal strength of the single gold nanowire plasmon waveguide, has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To address the aforementioned problems in existing technologies, the present invention aims to provide a method for optically modulating the morphology and enhancing the conduction of a single gold nanowire plasmonic waveguide. Starting with an initial gold nanowire synthesized via a polyol method, the morphology at the nanowire tip is controllably adjusted through photoinduced in-situ gold deposition. While maintaining the chemical stability and inherent optical properties of the gold nanowire, the coupling conversion efficiency between photons and surface plasmons at the nanowire tip is improved, thereby significantly enhancing the conduction performance of the plasmonic waveguide.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide includes the following steps:

[0009] 1) Gold nanowires were dispersed on the surface of a SiO2 / Si substrate to obtain a single dispersed gold nanowire sample.

[0010] 2) Perform oxygen plasma surface activation treatment on the single gold nanowire sample obtained in step 1) to remove the residual PVP coating layer on the surface of the gold nanowire.

[0011] 3) Add chloroauric acid aqueous solution to the surface of the gold nanowires treated in step 2);

[0012] 4) Focused continuous laser is used to irradiate one or both ends of a single gold nanowire. Under laser irradiation, Au ions in chloroauric acid are deposited at the ends of the gold nanowire, so as to achieve photo-induced control of the end morphology of the single gold nanowire.

[0013] Preferably, in step 1), the gold nanowires are prepared using the polyol method.

[0014] Preferably, in step 1), the length of the gold nanowire is 4~8μm.

[0015] Preferably, in step 1), the thickness of the SiO2 layer in the SiO2 / Si substrate is 400 nm.

[0016] Preferably, in step 2), the oxygen plasma treatment conditions are: gas pressure 0.35 mbar, power 50 W, and treatment time 15~40 s.

[0017] Preferably, in step 3), the concentration of the chloroauric acid aqueous solution is 1~10 mM. More preferably, the concentration of the chloroauric acid aqueous solution is 5 mM.

[0018] Preferably, in step 4), the wavelength of the focused laser is 640 nm.

[0019] Preferably, in step 4), the power of the focused laser is 0.1~0.5 mW. More preferably, the power of the focused laser is 0.3 mW.

[0020] Preferably, in step 4), the irradiation time of the focused laser is 1 to 8 minutes. More preferably, the irradiation time of the focused laser is 4 minutes.

[0021] Preferably, in step 4), the focused laser is a circularly polarized laser.

[0022] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0023] 1) This invention utilizes the surface plasmon propagation mode in a single gold nanowire to form a locally enhanced electromagnetic field at the end of the gold nanowire under laser excitation, and induces local enrichment of Au material to form a deposition structure, thereby realizing remote photoinduced control of the morphology of the gold nanowire end.

[0024] 2) This invention constructs a local field enhancement structure at both ends of a single gold nanowire by photo-induced in-situ gold deposition, thereby achieving controllable adjustment of the nanowire end morphology. The formed end structure can effectively enhance the local electromagnetic field, improve the coupling efficiency between incident light and surface plasmons and the radiation conversion efficiency of surface plasmons to photons at the output end, thereby significantly enhancing the output signal intensity of the single gold nanowire waveguide and improving the plasmon waveguide conduction performance.

[0025] 3) This invention achieves adjustable optimization of photoinduced deposition behavior and waveguide enhancement effect by controlling parameters such as laser power, excitation wavelength, irradiation time and chloroauric acid concentration, and has good process controllability and experimental repeatability; under 640nm laser excitation conditions, it can obtain better local field enhancement and waveguide enhancement effects, and the scattering intensity at the output end of the treated gold nanowire can be increased by 2.3 to 2.6 times, indicating that this invention can significantly enhance the plasmonic waveguide transmission capability of a single gold nanowire;

[0026] 4) The method of the present invention has the advantages of simple operation, mild experimental conditions, high local control precision and good repeatability, and is applicable to fields such as nanophotonic devices, on-chip optical interconnects, plasmonic integrated devices and nano-optical sensing. Attached Figure Description

[0027] Figure 1 Dark-field micrographs of the optically induced end-structure modulation of gold nanowires in chloroauric acid environment in Example 3; where a is before laser irradiation and b is after laser irradiation.

[0028] Figure 2The images show the scattering spectra of the left and right ends of nanowire 2 before and after photoinduced modulation in the chloroauric acid environment in Example 3; where a is the left end of nanowire 2 and b is the right end of nanowire 2.

[0029] Figure 3 The images are dark-field micrographs of gold nanowires before and after photoinduced modulation in Example 3; where a is a dark-field micrograph collected in air before adding chloroauric acid solution and laser irradiation, and b is a dark-field micrograph collected in air after photoinduced modulation, after rinsing with ultrapure water to remove residual chloroauric acid solution and drying.

[0030] Figure 4 The images show the scattering spectra of the left and right ends of nanowire 2 after photoinduced morphology modulation in Example 3; where a is the left end of nanowire 2 and b is the right end of nanowire 2.

[0031] Figure 5 Dark-field micrographs of gold nanowires before and after laser irradiation under chloroauric acid-free conditions in Comparative Example 1; where a represents before laser irradiation and b represents after laser irradiation.

[0032] Figure 6 The image shows SEM images of nanowire 4 before and after laser irradiation in Comparative Example 1; where ac represents before laser irradiation and df represents after laser irradiation.

[0033] Figure 7 The images show SEM images of nanowire 2 before and after laser irradiation; where ac represents before laser irradiation and df represents after laser irradiation.

[0034] Figure 8 The images show SEM images of nanowire 3 before and after laser irradiation; where ac represents before laser irradiation and df represents after laser irradiation.

[0035] Figure 9 The transmission diagrams are shown before and after photoinduced morphology modulation of nanowire 2 in Example 5; where a is before laser irradiation and b is after laser irradiation.

[0036] Figure 10 The image shows the transmission diagrams before and after photoinduced morphology modulation of nanowire 3 in Example 5; where a represents before laser irradiation and b represents after laser irradiation. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is further described below with reference to specific embodiments. Unless otherwise specified, the technical means used in the following embodiments are all conventional means well known to those skilled in the art. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer are followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0038] Unless otherwise stated, the laser power described in the embodiments of this application refers to the actual laser power incident on the sample surface after being transmitted through the optical system.

[0039] Example 1

[0040] This embodiment provides a method for preparing gold nanowires, the specific steps of which are as follows:

[0041] 1) Dissolve 0.45g of polyvinylpyrrolidone (PVP, average molecular weight 55000) in 10 mL of ethylene glycol and stir magnetically for 20 min at room temperature until completely dissolved to obtain a PVP-ethylene glycol solution. Then preheat in an oil bath at 150℃ for 15 min under nitrogen protection.

[0042] 2) Weigh 1.7 mg of silver nitrate and dissolve it in 5 mL of ethylene glycol to obtain a 2 mM silver nitrate ethylene glycol solution; then add the silver nitrate ethylene glycol solution to the PVP-ethylene glycol reaction system obtained in step 1), and mix for 5 min under low-speed magnetic stirring at 100 rpm to obtain a solution containing Ag. + The growth reaction system;

[0043] 3) Dissolve 9.8 mg of chloroauric acid tetrahydrate in 5 mL of ethylene glycol to obtain a 5 mM chloroauric acid glycol precursor solution;

[0044] 4) Keep the growth reaction system obtained in step 2) under the oil bath condition of 150℃, and use a syringe pump to add the chloroauric acid glycol precursor solution obtained in step 3) dropwise to the above reaction system at a rate of 0.3 mL / min. During the dropwise addition, keep the magnetic stirring at 100 rpm. After all the dropwise addition is completed, stop stirring and let it stand at 150℃ for 3 hours.

[0045] 5) After the reaction is complete, allow the mixture to cool naturally to room temperature. Add 20 mL of acetone to the reaction solution, mix well, centrifuge at 8000 rpm for 10 min, discard the supernatant, redisperse the precipitate with anhydrous ethanol, centrifuge and wash again, repeat the washing 3 times; disperse the purified product in 10 mL of anhydrous ethanol and sonicate for 5 min to obtain a gold nanowire dispersion.

[0046] Example 2: Construction of a single gold nanowire sample

[0047] 1) Base cleaning treatment

[0048] Thermally oxidized SiO2 (400 nm thick) / Si substrate was selected as the carrier substrate. Before use, it was ultrasonically cleaned with acetone, isopropanol and deionized water for 5 min each, dried with nitrogen, and then placed in an oxygen plasma cleaner for treatment. The treatment parameters were: pressure 0.35 mbar, power 50 W and treatment time 40 s.

[0049] 2) Gold nanowire dispersion

[0050] After appropriately diluting the gold nanowire ethanol dispersion prepared in Example 1, 5 μL was dropped onto the cleaned SiO2 / Si substrate surface and allowed to stand for a few seconds to spread naturally. Then, the substrate surface was rinsed with a small amount of ultrapure water to remove excess liquid and undeposited nanowires, and then gently dried with nitrogen gas. After treatment, a single gold nanowire sample uniformly dispersed on the substrate surface can be obtained.

[0051] 3) Target nanowire screening

[0052] The samples were scanned using a dark-field optical microscope to select target gold nanowires that met the following criteria: single, dispersed nanowires without cross contact, clearly distinguishable ends, length of 4–8 μm, and uniform dark-field scattering brightness. The position coordinates of the target gold nanowires were recorded for subsequent in-situ light manipulation experiments.

[0053] Example 3: Photoinduced morphology regulation in a chloroauric acid environment

[0054] 1) PVP removal treatment

[0055] The gold nanowire sample obtained in Example 2 was placed in an oxygen plasma cleaner again for treatment. The treatment parameters were: gas pressure 0.35 mbar, power 50 W, and treatment time 15 s, in order to remove the residual PVP coating layer on the surface of the gold nanowire.

[0056] 2) Construction of the chloroauric acid reaction system

[0057] 20 μL of chloroauric acid aqueous solution with a concentration of 5 mM was dropped onto the surface of the treated sample to make the droplet uniformly cover the target gold nanowire region, and then a clean coverslip was placed on top.

[0058] 3) Construction of a light-induced remote control system

[0059] An Olympus inverted dark-field microscope was used as the experimental platform, equipped with a 100× dark-field objective lens (Olympus, NA=0.8). A continuous laser with a wavelength of 640 nm was introduced into the microscope optical path via free-space coupling and then focused onto the end of the target gold nanowire by the objective lens after spatial filtering. The actual laser power incident on the sample surface was controlled to be 0.3 mW, and the laser polarization state was adjusted to circular polarization.

[0060] 4) Photoinduced morphology regulation process

[0061] A focused laser was used to irradiate both ends of the target gold nanowire, with each end irradiated for 4 minutes. During the laser irradiation, the gold nanowire generated local plasmon resonance under the excitation of the optical field, and a surface plasmon propagation mode was formed along the nanowire axis. At the same time, a local enhanced electromagnetic field was formed at the end of the gold nanowire, thereby promoting the local enrichment of Au material near the end of the nanowire and the formation of a deposition structure, realizing remote photoinduced control of the morphology of the end of a single gold nanowire.

[0062] Dark-field micrographs of gold nanowires on SiO2 / Si substrates before and after photo-induced treatment are shown below. Figure 1 As shown, nanowire 1 was not treated with laser irradiation, while nanowires 2 and 3 were treated with laser irradiation at both ends. Figure 1 It can be seen that after laser irradiation, the scattering brightness at both ends of nanowires 2 and 3 is significantly enhanced, while no significant change is observed in nanowire 1, which has not been irradiated by laser.

[0063] Dark-field scattering signals from the left and right ends of nanowire 2 before and after irradiation were collected using a 100× dark-field objective lens (Olympus, NA = 0.8). These signals were then coupled to a spectrometer (QE Pro, Ocean Optics) via a 50 μm aperture fiber for spectral acquisition and analysis. The test conditions were: irradiation with a circularly polarized continuous laser at a wavelength of 640 nm; the actual laser power applied to the sample surface was 0.3 mW; and the irradiation time was 4 min. The test results are as follows: Figure 2 As shown. By Figure 2 It can be seen that after laser irradiation, the intensity of the scattering peaks at both ends of nanowire 2 is significantly enhanced, accompanied by a certain degree of redshift.

[0064] 5) Sample cleaning

[0065] After laser irradiation, the coverslip was removed and the sample surface was immediately rinsed with ultrapure water to remove residual chloroauric acid solution and byproducts, and then dried with nitrogen gas for later use.

[0066] Dark-field micrographs of gold nanowires before and after photoinduced modulation, as shown below Figure 3 As shown. Among them, Figure 3 Image a is a dark-field micrograph acquired in air before the addition of chloroauric acid solution and laser irradiation; Figure 3 Image b is a dark-field micrograph acquired in air after photoinduced growth, following rinsing with ultrapure water to remove residual chloroauric acid solution and drying. Figure 3 It can be seen that the scattering brightness at both ends of the gold nanowire is significantly enhanced after photo-induced treatment, indicating that a new gold deposition structure is formed at the ends of the nanowire, resulting in enhanced local plasmon response at the ends.

[0067] Scattering spectroscopy was performed on nanowires 2 after washing and drying with ultrapure water. Scattering signals from the left and right ends of the nanowires 2 were collected using a 100× dark-field objective lens and coupled to a spectrometer via a 50 μm aperture fiber for spectral acquisition. The test conditions were: irradiation with a circularly polarized continuous laser at a wavelength of 640 nm, an actual incident laser power of 0.3 mW on the sample surface, and an irradiation time of 4 min. The test results are as follows: Figure 4 As shown.

[0068] Figure 4 a and Figure 4 In the figure, b represents the scattering spectra of the left and right ends of nanowire 2 in air. Figure 4 It can be seen that after photo-induced modulation, both ends of the nanowire have obvious scattering responses, and both ends of the nanowire maintain strong scattering responses, indicating that the formed end gold deposition structure still has stable local plasmon response characteristics in an air environment.

[0069] Comparative Example 1: Light Irradiation Control Experiment under Chloroauric Acid-Free Conditions

[0070] To verify the role of the chloroauric acid environment in the photoinduced end-structure regulation process, a control experiment was conducted without adding chloroauric acid solution.

[0071] The experimental procedure was basically the same as in Example 3, except that chloroauric acid aqueous solution was not added, and the target gold nanowires were irradiated with laser only in air. The laser used was a circularly polarized continuous laser with a wavelength of 640 nm. The actual laser power acting on the sample surface was 0.3 mW, and the irradiation time was 4 min. All other experimental conditions were the same as in Example 3.

[0072] Dark-field micrographs of gold nanowires on SiO2 / Si substrates before and after irradiation, as shown below Figure 5 As shown, nanowire 4 was not treated with laser irradiation, while nanowires 5 and 6 were treated with laser irradiation at both ends.

[0073] Depend on Figure 5 It can be seen that no significant changes were observed in nanowires 5 and 6 that were not subjected to laser irradiation, and no significant increase in scattering brightness was observed at both ends of nanowire 4 as in Example 3. The overall changes in the dark field images before and after irradiation were small.

[0074] Depend on Figure 6 It can be seen that no significant morphological changes were observed at the ends of nanowires 4 after laser irradiation in an air environment. These results indicate that laser irradiation alone is insufficient to achieve the end-structure modulation effect seen in Example 3, and that a chloroauric acid environment plays a crucial role in achieving photoinduced end-structure modulation.

[0075] Example 4: SEM morphology characterization before and after photoinduction

[0076] The morphology of gold nanowires before and after laser irradiation was characterized using scanning electron microscopy (SEM). The SEM images of nanowire 2 before and after irradiation are shown below. Figure 7 As shown; SEM images of nanowire 3 before and after irradiation are as follows. Figure 8 As shown. The experimental conditions were: 640 nm circularly polarized continuous laser, laser power 0.3 mW, and irradiation time 4 min.

[0077] Depend on Figure 7 and Figure 8 It can be seen that after laser irradiation, the ends of gold nanowires thickened significantly and underwent local morphological changes, indicating that Au atoms preferentially deposited and grew under the influence of a localized enhanced field.

[0078] Example 5: Test on the enhancement of gold nanowire waveguide propagation before and after photo-induced waveguide propagation

[0079] To verify the effect of photoinduced morphology modulation on the plasmonic waveguide conduction performance of gold nanowires, waveguide conduction tests were performed on the treated single gold nanowires.

[0080] The experiment used a 640 nm continuous laser as the excitation source, which was introduced into an Olympus inverted dark-field microscope system via free-space coupling. The laser was focused on one end of the target gold nanowire using a 100× dark-field objective (Olympus, NA = 0.8) to excite surface plasmon resonance (SPP) modes. The laser power was set to 0.6 mW, and the laser light was linearly polarized, with the polarization direction parallel to the long axis of the gold nanowire. The excited SPP propagated along the axial direction of the gold nanowire and was finally coupled out as scattered light at the other end of the nanowire. A CCD was used to record the light conduction state in the gold nanowire in real time. The light conduction image after photoinduced modulation of the nanowire is shown below. Figure 9 As shown; the conduction image after photoinduced modulation of nanowire 3 is as follows. Figure 10 As shown.

[0081] Depend on Figure 9 and Figure 10 It is evident that the photo-induced gold nanowires exhibited significantly enhanced scattering output signals at their output ends, indicating improved plasmon waveguide conduction performance. This enhancement is primarily attributed to the structural modulation effect formed by photo-induced gold deposition at both ends of the gold nanowires. On one hand, the modulated input end enhances the local electromagnetic field, increasing the coupling efficiency of incident light to surface plasmons; on the other hand, the modulated output end enhances the radiative conversion capability of surface plasmons to free-space light, thereby obtaining a stronger output scattering signal.

[0082] The above results show that the present invention achieves controllable adjustment of the structure at both ends of the gold nanowire through photo-induced method, effectively improving the coupling efficiency of light to surface plasmons at the incident end and the conversion efficiency of surface plasmons to photons at the emitting end, thereby enhancing the plasmon waveguide transmission performance of a single gold nanowire.

[0083] Example 6: The effect of different laser powers on the enhancement effect of optically induced waveguides

[0084] Irradiation experiments were conducted on single gold nanowires using different laser powers. The experimental procedures were basically the same as in Example 3, except that the actual incident laser power on the sample surface was set to 0.1 mW, 0.3 mW, and 0.5 mW, respectively. The other experimental conditions remained the same, including: laser wavelength of 640 nm, laser polarization state of circular polarization, irradiation time of 4 min, and HAuCl4 solution concentration of 5 mM.

[0085] During the experiments, a 100× dark-field objective lens (Olympus, NA = 0.8) was used to focus the laser onto both ends of the target gold nanowires, and the scattering changes of the nanowires were observed in real time using a dark-field microscope. The scattering spectra at the output ends of the nanowires were acquired using a QEPro spectrometer. Five different gold nanowires were randomly selected for each experiment, and the average value and standard deviation were calculated. The results are shown in Table 1.

[0086] Table 1. Waveguide enhancement results under different laser powers

[0087]

[0088] As shown in Table 1, moderate laser power is beneficial for forming a stable and uniform local deposition structure, thereby improving the enhancement effect of plasmonic waveguide; excessive power can easily lead to enhanced local photothermal effect, causing instability in the local morphology of nanowires.

[0089] Example 7: Effect of different irradiation times on the enhancement effect of optically induced waveguides

[0090] Experiments were conducted using different irradiation times. The experimental steps were basically the same as in Example 3, except that the laser irradiation times were set to 1 min, 4 min, and 8 min, respectively. The other experimental conditions remained the same, including: laser wavelength of 640 nm, laser power of 0.3 mW, laser polarization state of circular polarization, and HAuCl4 solution concentration of 5 mM.

[0091] The scattering spectra at the output end were acquired using a QEPro spectrometer. Five different gold nanowires were randomly selected for each experiment and the average value was calculated. The morphological changes at the ends of the nanowires were observed using SEM. The results are shown in Table 2.

[0092] Table 2. Effects of different irradiation times on waveguide enhancement

[0093]

[0094] As shown in Table 2, the optically induced morphology control method of the present invention has good time controllability, and the 4 min time can balance morphology uniformity and waveguide enhancement effect.

[0095] Example 8: The effect of different excitation wavelengths on the enhancement effect of optically induced waveguides

[0096] Experiments were conducted using continuous lasers of different wavelengths. The experimental procedures were basically the same as in Example 3, except that the excitation laser wavelengths were 532 nm, 640 nm, and 785 nm, respectively. The other experimental conditions remained the same, including: laser power of 0.3 mW, laser polarization state of circular polarization, irradiation time of 4 min, and HAuCl4 solution concentration of 5 mM.

[0097] The scattering spectra at the output end were acquired using a QEPro spectrometer. Five different gold nanowires were randomly selected for each experiment and the average value was calculated. The morphological changes at the ends of the nanowires were observed using SEM. The results are shown in Table 3.

[0098] Table 3. Waveguide enhancement results of different excitation wavelengths

[0099]

[0100] As shown in Table 3, there is a clear matching relationship between the excitation wavelength and the plasmon resonance mode of gold nanowires. Among them, the 640 nm condition can obtain better local field enhancement and waveguide enhancement effects.

[0101] Example 9: Effect of different HAuCl4 concentrations on the enhancement effect of optically induced waveguides

[0102] Experiments were conducted using HAuCl4 solutions of different concentrations. The experimental procedures were basically the same as in Example 3, except that the concentrations of the HAuCl4 aqueous solution were set to 1 mM, 5 mM and 10 mM, respectively. The other experimental conditions remained the same, including: laser wavelength: 640 nm, laser power: 0.3 mW, laser polarization state: circular polarization, irradiation time: 4 min, and objective lens: 100× dark field objective lens (NA=0.8).

[0103] After the experiment, dark-field microscopy was used to observe the scattering changes at the output end of the nanowires, and SEM was used to characterize the morphology of the nanowire ends. A QEPro spectrometer was used to collect the scattering spectra at the output end of the nanowires. Five different gold nanowires were randomly selected for each experiment, and the average values ​​were calculated. The results are shown in Table 4.

[0104] Table 4 Waveguide enhancement results at different HAuCl4 concentrations

[0105]

[0106] As shown in Table 4, although 10 mM yields higher scattering intensity, SEM images show significant agglomeration and irregular thickening, leading to decreased structural stability. Therefore, considering both morphological uniformity and waveguide stability, 5 mM is the preferred concentration.

[0107] Comparative Example 2

[0108] To verify the effect of laser irradiation, a control experiment without laser irradiation was set up. The experimental procedure was basically the same as in Example 3, including: treating the gold nanowires with oxygen plasma; adding 20 μL of 5 mM HAuCl4 solution; and covering with a coverslip. The difference was that no laser irradiation was performed, and the samples were simply left to stand at room temperature for 4 min.

[0109] The scattering spectra at the output end were acquired using a QEPro spectrometer. Five different gold nanowires were randomly selected for each experiment and the average value was calculated. The morphological changes at the ends of the nanowires were observed using SEM. The results are shown in Table 5.

[0110] Table 5. Test results of Comparative Example 2

[0111]

[0112] As shown in Table 5, the scattering intensity at the output end of the gold nanowire did not show a significant increase under laser-free conditions, and no obvious local deposition structure was observed in the SEM results. This indicates that laser excitation is an important condition for realizing the photoinduced morphology control and plasmonic waveguide enhancement of this invention.

[0113] Comparative Example 3

[0114] To verify the effect of the PVP coating layer on the surface of gold nanowires on photoinduced morphology regulation, a control experiment was set up with PVP not removed. The experimental procedures were basically the same as in Example 3, except that the oxygen plasma treatment step was omitted, i.e., the residual PVP layer on the surface of the gold nanowires was not removed. The other experimental conditions remained the same, including: HAuCl4 concentration of 5 mM, laser wavelength of 640 nm, laser power of 0.3 mW, and irradiation time of 4 min.

[0115] The scattering spectra at the output end were acquired using a QEPro spectrometer. Five different gold nanowires were randomly selected for each experiment and the average value was calculated. The changes in the morphology of the nanowire ends were observed using SEM. The results are shown in Table 6.

[0116] Table 6 Test Results of Comparative Example 3

[0117]

[0118] As shown in Table 6, the residual PVP coating layer hinders the local enrichment of Au on the surface of the gold nanowires, thereby reducing the local field enhancement and plasmon waveguide enhancement effects. Surface activation treatment of the gold nanowires is beneficial to improving the photoinduced morphology control efficiency of this invention.

[0119] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for optically modulating the morphology and enhancing the conduction of a single gold nanowire plasmonic waveguide, characterized in that, Includes the following steps: 1) Gold nanowires were dispersed on the surface of a SiO2 / Si substrate to obtain a single dispersed gold nanowire sample. 2) Perform oxygen plasma surface activation treatment on the single gold nanowire sample obtained in step 1) to remove the residual PVP coating layer on the surface of the gold nanowire. 3) Add chloroauric acid aqueous solution to the surface of the gold nanowires treated in step 2); 4) Focused continuous laser is used to irradiate one or both ends of a single gold nanowire. Under laser irradiation, Au ions in chloroauric acid are deposited at the ends of the gold nanowire, so as to achieve photo-induced control of the end morphology of the single gold nanowire.

2. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 1), the gold nanowires are prepared using the polyol method.

3. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 1), the length of the gold nanowires is 4~8μm.

4. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 1), the thickness of the SiO2 layer in the SiO2 / Si substrate is 400 nm.

5. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 2), the oxygen plasma treatment conditions are: gas pressure 0.35 mbar, power 50 W, and treatment time 15~40 s.

6. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 3), the concentration of the chloroauric acid aqueous solution is 1~10 mM.

7. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 4), the wavelength of the focused laser is 640 nm.

8. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 4), the power of the focused laser is 0.1~0.5 mW.

9. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 4), the irradiation time of the focused laser is 1 to 8 minutes.

10. The method for optically modulating the morphology and conduction enhancement of a single gold nanowire plasmonic waveguide according to claim 1, characterized in that, In step 4), the focused laser is a circularly polarized laser.

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